This invention relates generally to thermostatic expansion valves for controlling refrigerant flow through a refrigeration system and particularly to a thermostatic expansion valve having a replaceable cartridge to change the capacity of the valve by providing a selected predetermined valve port for the valve.
It is sometimes necessary to change the capacity of a thermostatic expansion valve in the field. In addition, valves which have become inoperative often require complete replacement. In both instances replaceable cartridge thermostatic expansion valves have become popular. In the first instance, the use of a replacement cartridge permits the capacity of the valve to be changed without completely disassembling the valve. In the second instance, the use of a replaceable cartridge valve allows the field service mechanic to carry one type of basic valve and a set of variable cartridges and adjust the capacity by selecting a suitable cartridge for the basic valve in the field.
Replaceable cartridge thermostatic expansion valves have been in use for many years and those currently used suffer from some disadvantages. Typical of the prior art type of replaceable cartridge valve commonly in use is that manufactured by Danfoss, Inc. of Mahawa, N.J. as valve T2/TE2 and disclosed in its Instruction Sheet R1.01.VA.22 dated April 1987. The same or closely similar valve is also manufactured by Alco Controls Division, Emerson Electric Co. of St. Louis, Mo. as valve T1 and disclosed in its Catalog Sheet T1 Series Thermo R Expansion Valve dated June 1991. Both of these publications are incorporated by reference herein. This type of valve has the cartridge mounted in the inlet connection and utilizes a single pushrod leading from the diaphragm to engage the spring-loaded valve pin located in the cartridge. This arrangement results in a direction of refrigerant flow in the closing direction of the valve pin which tends to provide poor modulation. In addition, in this prior art valve the diaphragm assembly power element is integral with the valve body and the location of the superheat adjustment spring assembly directly below the diaphragm results in the spring assembly acting directly on the diaphragm. Accordingly, the diaphragm has to be compressed when assembling the valve and is not removable which has the disadvantage that it limits flexibility of the valve body in the field. Moreover, the superheat spring is adjusted by a force applied by an inclined, eccentrically located adjustment screw rather than by an axially located adjustment screw.
Another disadvantage of this construction is that the additional spring used to keep the pin in contact with the pushrod is very lightly loaded and provides little force to overcome contamination in the pin and port area. Moreover, the location of the cartridge in the inlet connection requires that it be held in place by a flare nut which leads to several problems. For example, if the nut is overtightened the stroke of the valve is increased such that the valve will not operate properly and the pin may not be properly seated. Also the valve cannot be made in a solder type connection, which is increasingly being used because it provides a leak free connection.
Another thermostatic expansion valve having a replaceable cartridge is disclosed in U.S. Pat. No. 2,327,542. In this valve the cartridge is transversely mounted relative to the valve inlet and the axis of the diaphragm and is housed within a removable screw. The cartridge includes a restricted orifice of predetermined diameter which does not cooperate with a valve pin.
The present replaceable cartridge valve overcomes these and other problems in a manner not disclosed in the known prior art.